1. Field of the Invention
The present invention relates to methods and apparatus using a directed energy beam to selectively deposit material from a gas phase to produce a part.
2. Conventional Part Production
The economies associated with conventional part production methods are related to the quantity of parts to be produced and the desired material characteristics of the finished parts. For example, large scale manufacture casting and extrusion techniques are often cost effective on extended production runs, but these production methods are generally unacceptable for small quantities, i.e., replacement parts or prototype production. A principal reason is the expensive part-specific tooling required by many such conventional part production methods. Even standard powder processing requires a die for shaping the powder, making powder processing unattractive as a method for producing a small number of parts.
Where only a small number of parts are desired, conventional production methods involving a subtractive machining method are usually used to produce the desired part. In such subtractive methods, material is cut away from the starting block of material to produce a more complex shape. Examples of subtractive machine tool methods include: milling, drilling, grinding, lathe cutting, flame cutting, electric discharge machining, etc. While such conventional machine tool subtractive methods are usually effective in producing the desired part, they are deficient in many respects.
First, such methods produce a large amount of waste material for disposal. Second, such machine tool methods usually involve a large initial expense for setting up the proper machining protocol and tools, a process which is not only expensive, but relies a great deal on human judgment and expertise. The cost-per-part increases, of course, when only a small number of parts are to be produced.
Another difficulty associated with such conventional machining techniques involves tool wear, which not only involves the cost of replacement, but also reduces machining accuracy as the tool wears. The accuracy of any part produced by conventional machining techniques is related to the tolerance limits inherent in the particular machine tool used. For example, in a conventional milling machine or lathe, the lead screws and ways are manufactured to certain tolerances, which initially limit the accuracy obtainable in manufacturing a part on the machine tool; tool wear effectively widens tolerances and thus further limits accuracy.
A further problem associated with conventional machine tool subtractive processes is the difficulty or even impossibility of making many part configurations. For example, conventional machining methods are usually best suited for producing symmetrical parts and parts where only the exterior surface is machined. Where a desired part is irregular in shape or has internal features, the machining becomes more difficult; quite often, the part must be divided into segments for production. In some cases, a particular part configuration cannot be made by conventional subtractive machining processes because of limitations imposed on machine tool placement.
Additive machining processes such as plating, cladding, and some welding processes, wherein material is added to a starting substrate, may supplement or replace subtractive machining in some applications. Recently developed additive-type machining methods use a laser beam to coat or deposit material on a starting article. Examples are disclosed in U.S. Pat. Nos. 4,117,302; 4,474,861; 4,300,474; and 4,323,756. These recent uses of lasers have been primarily limited to adding a coating to a previously machined article. Often, such laser coating methods have been employed to achieve certain metallurgical properties unobtainable by any other methods. Typically, laser coating involves rotating the starting article while the laser is directed at a fixed location, the coating material being spray-coated onto the article so that the laser will then melt the coating onto the article.
Laser sintering of a powder is disclosed in U.S. Pat. No. 4,863,538, and a process for compressing a powder-based material into a coherent mass prior to sintering is suggested in U.S. Pat. No. 4,752,352. Previously suggested selective sintering methods, however, are associated with the problem of evenly depositing the layers of powder for sintering.